Apparatus utilizing a foam to absorb gaseous pollutants or filter particulate matter from a gas are well-known. Generally, they comprise a treatment chamber containing a foam layer therein spaced between a dirty gas inlet and a cleaned gas outlet. Such a scrubber is disclosed in U.S. Pat. No. 3,616,610. These devices are used to clean a variety of gases, particularly those issuing from industrial operations.
A critical feature in proper operation of such foam scrubbers is the maintenance of an optimum composition of the foam layer. If the foam layer is either too wet or too dry the proper pressure drop is not obtained and proper scrubbing is not possible. The foam layer density is difficult to control, particularly in the case of synthetic based foaming agents. Such foams tend to constantly dry out and eventually expand and are blown out of the dry treatment chamber by the gas. When the layer has become dry, foam density decreases, the concentration of foaming agent in the layer rises, the pressure drop across the layer falls, and the foam layer begins to uncontrollably expand.
While electrode sensors have been utilized to detect a low foam layer height and addition of fresh foam then made to increase layer height, no satisfactory means or method have been found to control excessive foam layer overexpansion.